Cyber Resilience

CVE-2025-5270

Mozilla Firefox ≤ 139.0

Published
27 May 2025
Modified
17 June 2026
Patch / advisory
View advisory
CVSS Score v3.1 7.5
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
EPSS Score 0.0025 17th percentile
Risk Priority 56 floored blend · peak EPSS

Summary

CVE-2025-5270 is a high-severity Cleartext Transmission of Sensitive Information (CWE-319) vulnerability in Mozilla Firefox. Its CVSS base score is 7.5 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Network Sniffing (T1040); ranked at the 17th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified map to SC-8 (Transmission Confidentiality and Integrity) — see the control section below for these in your framework.

OWASP Top 10 for Web (2025)

A04:2025 Cryptographic Failures

EU & UK References

Vulnerability Data

In certain cases, SNI could have been sent unencrypted even when encrypted DNS was enabled. This vulnerability was fixed in Firefox 139 and Thunderbird 139.

CWE(s)
CWE-319

Related Threats

MITRE ATT&CK Enterprise Techniques

T1040 Network Sniffing Credential Access
Adversaries may passively sniff network traffic to capture information about an environment, including authentication material passed over the network.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2024-4765Same product: Mozilla Firefox
CVE-2023-25740Same product: Mozilla Firefox
CVE-2024-11703Same product: Mozilla Firefox
CVE-2025-54143Same product: Mozilla Firefox
CVE-2025-6427Same product: Mozilla Firefox
CVE-2026-16406Same product: Mozilla Firefox
CVE-2026-24868Same product: Mozilla Firefox
CVE-2026-16394Same product: Mozilla Firefox
CVE-2026-8401Same product: Mozilla Firefox
CVE-2023-37206Same product: Mozilla Firefox

Affected Assets

mozilla
firefox
≤ 139.0

Mitigating Controls

Mitigating Controls (NIST 800-53 r5) AI

SC-8 Transmission Confidentiality and Integrity good match

SC-8 directly requires protecting confidentiality of transmitted information, which structurally eliminates cleartext transmission of sensitive data.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.DS-02 full match
prevents

Encryption of data-in-transit directly prevents cleartext transmission while the control also addresses integrity and availability.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.21 Security of network services mostly match
prevents

Specifying encryption and other security technology for network services prevents transmission of sensitive information in cleartext over potentially untrusted channels.

A.5.14 Information transfer partial match
prevents

Mandating cryptographic protection and stronger authentication on public networks stops the transmission of plaintext sensitive information.

A.6.7 Remote working partial match
mitigates

Specifying communications-security requirements and secure remote-access methods (including encryption expectations) prevents the transmission of sensitive data in cleartext over home or public networks.

A.7.12 Cabling security partial match
mitigates

Armoured conduits, electromagnetic shielding and locked enclosures make passive eavesdropping on unencrypted traffic traversing the cables more difficult, mitigating exposure of sensitive data in transit.

References